Sin.

Sin never slew a soul unless there went
Along with it some tempting blandishment.

Sin once reached up to God's eternal sphere,
And was committed, not remitted there.

There's no constraint to do amiss,
Whereas but one enforcement is.

After true sorrow for our sins, our strife
Must last with Satan to the end of life.

Sin no existence; nature none it hath,
Or good at all, as learned Aquinas saith.

When once the sin has fully acted been,
Then is the horror of the trespass seen.